The heart of the DSe is her battery array. Composed of 12-volt Enersys AGM-style batteries, the resulting banks have 200 Amp Hours/48v each (20 kW Hours total). We bench tested this array for months - charging - discharging - charging - discharging - over-charging - running down to zero. Our tests conclude that the batteries will provide up to 1,000 discharges. Each battery array is fed by its own Outback MPPT FX60 controller/charger which in turn is fed by a 3 kW section of the solar array. We use the same “bullet-proof” batteries for the 12 vDC system and for diesel starting batteries. The 12v system is charged by DC/DC chargers from the main battery arrays.

To get the maximum amount of current from a solar array, we use state of the art MPPT (Maximum Power Point Tracking) controller/chargers from Outback. These controllers optimize the match between the PV array and the battery bank, getting every watt of available power. Note: All these installations are temporary for the trials ONLY.

For purposes of this sea trial we used the water-cooled Ossa Powerlite 35 HP motors. These gave us the performance figures through our electric-mode speeds and beyond to 9+ knots. Production DSes will be fitted with the Steyr Hybrids and sail drives which will produce similar electric performance at displacement speeds.

Each production DSe will be fitted with the Steyr Serial Hybrid Propulsion System fitted with a ZF saildrive. The Steyr diesel delivers 75 HP. The green “bell-housing” (pictured right) houses a 5 kW flywheel generator/7 kW motor. In diesel mode, the hybrid portion acts as a generator and passes power through to the saildrive. In electric mode, the hybrid portion disengages from the diesel and powers the saildrive directly.

Each Hybrid drive has its own 10 kW hour/48v battery array. This array is charged from shore power (the grid), 3 kW solar array and the 5 kW generator. Away from the dock, all of the DSe’s electrical needs are in turn fed from these battery arrays. In electric mode, the Hybrid 7 kW motor gets it’s power from the batteries which, in turn, are being constantly charged , during daylight, by the solar array.

How We Tested. We made dozens of runs up river (against tide and wind) and down - with sun and without - with rain - with 4 different sets of propellers and 3 different load conditions. We took readings of current in from the solar array, current out to the motors and current at the batteries. All up river runs were immediately followed by down river ones, in the same section of the river to make averaging accurate. The speed shown to right is from Trane’s cell phone (which tended to agree closely to a Garmin handheld). This speed of 7.39 knots would be from one run and averaged later. The ammeter at the bottom is reading the amps being used by one motor (13.43 A) - this is multiplied by the system volts to get the watts being used at any given time.

George Petie, N.A., takes careful notes of all the data generated by the days of water trials. At the end of each day, the data was tallied, averaged, entered into a spreadsheet for analysis. The first graphic representations confirmed that our key goals had been met - the DSe Hybrid will cruise at speeds up to 6 knots in equilibrium - power in from solar equal to power out to the motors!

Sea Trials Conducted by Capt. Bill Pike for Power & Motoryacht.

This October, Captain Bill Pike, came to Biscayne Bay to conduct thorough boat review and sea trials for an upcoming article in Power and Motoryacht January issue (on the stands in December, 2008).

A full series of speed runs were made with averages calculated between each pair of runs - both electric and diesel. The graph to the right is a result of these trials.

1. The DSe will be able to run in electric mode up to 6 knots using about 5kW per motor.

2. In diesel mode, we reach a top speed of 9 plus knots with an optimum cruise of 7 knots.

3. The Steyr diesel emits the least emissions of any marine diesel in her class. She can also cleanly burn not only diesel, but kerosene, heating oil, cooking oil and of course, Bio-Diesel.

SUMMARY OF SEA TRIALS. If there were CAFE standards for motor yachts, the DSe Hybrid would be at the top of the list! With a potential of infinite range at speeds up to 4-1/2 knots and a diesel range of 500 NM on only 100 gallons  (20 gallons in reserve) at 7 knots. (Tests will be done shortly with a quasi-diesel-electric mode, running one diesel and one electric motor. At 6 knots, we anticipate an economic boost of about 50%, depending on the amount of sun available). Since the Island Pilot DSe Hybrid’s goal is to be the most efficient, most environmentally-friendly motor yacht, we have chosen to outfit her with just enough power to go efficiently at displacement speeds. She has an extremely efficient cruise of 7 knots burning only 1.4 gallons per hour. One other advantage of the Steyr Serial Hybrid Propulsion System: you have 4 motors! Think about it. 3 motors can fail and you still have a way to get home. No other yacht has this amount of redundant “Get-Home” power options.

Bill Pike driving the DSe 12m during sea trials in October. Notice the lack of a steering wheel - the DSe is controlled with a Fly-by-Wire system from Tecnautic.